1. Field of the Invention
The present invention relates to a light source device and a projector including the light source device.
2. Description of the Related Art
Nowadays, data projectors are often used as image projection apparatuses for projecting a display image of a personal computer, a video image, an image based on image data stored in a memory card or the like onto a screen. In such a projector, light emitted from a light source is condensed on a micromirror display device called a DMD (Digital Micromirror Device) or a liquid crystal panel so as to display a color image on a screen.
Conventionally, use of high-luminance discharge lamps as light sources in such projectors has become the mainstream. In recent years, however, there have been many developments or proposals using light emitting diodes, laser diodes, organic ELs, phosphor emissions, etc. as light sources. For example, JP-A-2004-341105 discloses a light source device including a solid-state light source for emitting ultraviolet light as excitation light and a fluorescent wheel consisting of a disc-like transparent substrate on which there is disposed a fluorescent substance layer for receiving the ultraviolet light emitted as excitation light and converting the ultraviolet light into visible light.
According to the disclosure of JP-A-2004-341105, a visible light reflective film for transmitting ultraviolet light and reflecting visible light is formed on a wheel surface of the fluorescent wheel on which the ultraviolet light will be incident. Thus, the fluorescent substance layer disposed on the emission-side wheel surface is irradiated with the incident ultraviolet light to generate fluorescent light and emit the fluorescent light to the emission side. At the same time, fluorescent light emitted to the incident surface side from the fluorescent substance layer is also reflected to the emission side by the visible light reflective film. Thus, the quantity of fluorescent light emitted from the fluorescent wheel can be increased.
In addition, in order to prevent optical components from being damaged by irradiation with excitation light, for example, a blue laser diode which emits blue wavelength light as excitation light may be used as the solid-state light source of the aforementioned light source device. In this case, the fluorescent wheel is configured to have a diffusion layer formed on the wheel surface so that the blue wavelength light transmitted by the fluorescent wheel can be used as it is.
A reflective film for transmitting blue wavelength light and reflecting any other visible light has to be formed on the incident surface of the fluorescent wheel for use in such a light source device. Manufacturing the light source device therefore becomes labor-consuming, causing increase in cost.
To solve the problem, a light source device can be conceived to have the following configuration. That is, a wheel substrate is formed out of a metal plate or the like so that blue wavelength light serving as excitation light and fluorescent light including red and green wavelength lights and emitted from fluorescent substances can be reflected by a reflective surface of the metal plate. Thus, blue, green and blue wavelength lights are emitted in turn.
However, when optical paths of the red, green and blue wavelength lights are made to be one and the same in such a case, the blue wavelength source light is reflected and mixed with the red or green wavelength fluorescent light which emits when the red or green fluorescent substance layer is irradiated with the blue excitation light. Therefore, there may be a problem that color purities deteriorate.
In addition, since the incidence surface and the emission surface of the blue wavelength light in the fluorescent wheel are one and the same, there is a problem that special configuration of an optical layout or an optical component is required for separating an optical path for incidence of the blue source light from an optical path for emission of the blue source light.